In wavelength division multiplexing (hereinafter also referred to as `WDM`) optical transmission systems, various network systems, e.g., a point-to-point system, an optical cross connect system and an optical ADM ring system, are constructed. Using already-installed transmission lines and equipment and the economization of the networks into account, optical transmission systems of this type need to transmit optical signals with various bit rates, e.g., 600 Mb/s, 2.4 Gb/s, 10 G/s while wavelength-multiplexing them using the already-installed transmission lines and equipment.
In this case, each node conducts linear-repeating to the next-stage node regardless of the bit-rate difference. However, it is known that the maximum transmission repeating distance (linear repeating distance) is limited due to a loss, a dispersion etc. in transmission line and depends upon the bit rate.
Because of this, the conventional WDM optical transmission systems have been designed considering previously the bit rates and repeat numbers of wavelength components to be received by the respective nodes.
However, the transmission system that the bit rate and repeat number are previously designed and fixed may not be flexibly applicable to the change of bit rate etc. to be required by an increase in transmission capacity. Then, the cost performance, reliability etc. of the network must be reduced that much.